Reproducing apparatus



Oct. 1, 1963 R. B. com-EN ET AL REPRODUCING APPARATUS 11 sheets-shea 1 Filed Sept. 2, 1959 n Oct. 1, 1963 R. B. coLTEN ETAL l105,907

REPRODUCING APPARATUS `Filed sept. 2, 1959 11 sheets-sheet 2 IN VEN T ORS' Oct. 1, 1963 R. B. com-EN ETAL 3,105,907

REPRODUCING APPARATUS Filed Sept. 2, 1959 l1 SheetS-Shet 3 CZ/Q/VEY Oct. 1, 1963 R. B. coLTEN ETAL 3,105,907

REPRODUCING APPARATUS Filed Sept. 2, 1959 l1 Sheets-Sheet 4 A TTOR/VEY Oct. l, 1963 R. B. COLTEN ETAL REPRODUCING APPARATUS Filed Sept. 2, 1959 1l Sheets-Sheet 5 Oct. 1, 1963 R. B. com-EN ETAL 3,105,907

REPRODUCING APPARATUS Filed Sept. 2, 1959 11 Sheets-Sheet 6 P, V i l I 50M :sf/Pvc MAA/0M :vez l ,ma/nf@ Oct. l, 1963 R. B. coLTEN ETAL 3,105,907

REPRODUCING APPARATUS Filed sept. 2, 1959 l1 Sheets-Sheet '7 IN VEN T ORS' OC- 1, 1963 R. B. coLTEN ETAL 3,105,907

REPRODUCING APPARATUS Filed Sept. 2, 1959 1l Sheets-Sheet 8 IN VEN T ORS Oct. l, 1963 R. B. cou-EN ETAL 3,105,907

REPRODUCING APPARATUS Filed sept. 2, 1959 11 sheets-sheet 9 @ff ff M74 mww Oct. 1, 1963 R. B. coLTEN ETAL REPRODUCING APPARATUS 1l Sheets-Sheet 10 Filed Sept. 2, 1959 ATTORNEY Oct. 1, 1963 R. B. coLTEN ETAL 3,105,907

REPRODUCING APPARATUS Filed Sept. 2, 1959 11 Sheets-Sheet l1 f IIIIIIIIII if IN V EN TORS A Nwe/wmf United States Patent O REPRGDUCING APPARATUS Robert B. Colteu, Dak Park, Mich., Glenn E. Wanttaja, Hales Corners, Wis., and August F. Scarpelli, Warren, Mich., assignors to General Motors Corporation,

Detroit, Mich., a corporation of Delaware Filed Sept. 2, i959, Ser. No. 837,697 34- Claims. (Cl. Z50- 292) This invention relates to improvement in reproducing apparatus adapted, although not exclusively, for machining reproductions of contours from a pattern on a workpiece.

In general, since reproducing apparatus must function rapidly and accurately, automatic operation is preferred, manual operation being slow and inaccurate, even though the operator has a high degree of skill. But for automatically operating reproducing apparatus to be eifective, i.e., versatile and adaptable for different applications, it must be capable of accomplishing without complexity at least as many operations as can be achieved with manual apparatus. For example, automatically operating reproducing apparatus should desirab-ly be capable of copying lines from a drawing or a blueprint as distinguished from expensively formed master drafts, be capable of following irregular contours without the `copying tool leading or lagging the tracer mechanism so as to induce errors into the iinal result, be uniniluenced by lines intersecting those to be copied, be capable of being placed on-course quickly and any extreme olf-course errors should not be permitted to destroy the workpiece, and be stable and instantaneously responsive and devoid of influence from speed uctua-tions.

With the foregoing in mind, the invention contemplates an automatically operating reproducing apparatus that is capable of copying irregular contours rapidly and accurately, that has a unique arrangement for copying a selected one of a series of intersecting lines, that lprovides novel modes both of getting on-course quickly and of stopping the apparatus when oit-course, that has provision for removing speed .fluctuations and inducing stability into the system, and for instantly responding .with constant speed operation, that is particularly suited for copying from any type master draft, that accommodates different size workpieces so mounted as to inhibit the influence of vibrations, eg., copying tool chatten and that may be adjusted for different size cutting tools.

Because it is desirable to copy from almost any type master draft such as blueprints, photastats, etc., a tracer mechanism for the automatic reproducing apparatus often utilizes some form of radiant energy to produce information pulses, e.g., photocells may be employed to sense olf-course errors and develop corresponding error signals. The photocells when used in pairs frequently, although identical, have different outputs at times when the outputs thereof should Ibe balanced to indicate no oit-course error. Moreover, when the photocells are rbalanced for one condition of lighting and reliectivity, they are often out of balance -when these condi-tions change. The outputs from these photocells must be picked up in such a manner as to be free of noise and these signals must aiford both correotions for parallel misalignments and lateral displacements relative to the contour bein-g traced. The development of these error signals as well as some provision for causing the copying tool to be maneuvered in accordance therewith, also present problems.

Accordingly, the invention provides the reproducing apparatus with a unique tracer mechanism that incorporates photosensitive means for detecting both parallel misalignments and lateral 'deviations thereof with respect to a contour to be traced, that has an unusual system for resolving these signals and causing an equivalent signal to be ICC developed for controlling movement of the copying tool, that eliminates noises during pickup of the error signals, and that has a novel mode of Calibrating the photosensitive means for ldifferent lighting conditions and master drafts of different degrees of reflectivity.

Although automatic control is desired, the apparatus should lbe capable of manual control at certain times, erg., provision should be made for preparing the apparatus manually for automatic operation without any excessive loss in time. With both manual and automatic controls available, then both must b'e coordinated so as to insure against the possibility of one system leading or lagging the other such that a workpiece could -be ruined. Also, in pursuing a certain cont-our, it may become necessary to maintain a selected course despite the tendency for the automatic control to demand otherwise.

Therefore, the invention incorporates both manual and automatic controls so coordinated as to be synchronized and permit either automatic or manual control at any time without concern for any lost motion due to leading or lagging between the two controls. Also Iby the invention, under critical operating conditions as when crossing intersecting lines, the existing course can be maintained without the intersecting line inuencing the operation.

When the reproducing apparatus is of considerable size, or when it is necessary to position the controls such that the operation of the copying tool relative to the workpiece is difficult to observe Aby the operator, or when personal safety prevents close observation of the apparatus, it becomes ydifficult to view the relative movements between the copying tool and the workpiece.

For this reason, the invention provides an operator control stat-ion, remotely positioned from the apparatus, with an unusual system for visually observing the performance of the copying tool.

In promoting accuracy of the finished contour, chips removed during machining operation can produce interference as well as obscure the cutting action if a substantial amount of metal is being removed. To overcome this problem, the invention affords a mode of quickly withdrawing removed chips from the cutting area. Specifically, the invention employs a vacuum pressure system for removing the chips from the proximity of the cutting tool and the workpiece through the spindle of the cutting tool.

Generally, reproducing apparatus employs a table or the equivalent of a size adequate to accommodate the largest master draft for which the apparatus'is designed. Necessarily, the `draft table will be of a relatively large size, and therefore, when small drafts as well as small drawings are to be traced, it is advantageous if the small drawing can he positioned anywhere on the draft table. This permits several such small drawings to be simultaneously attached to the drafty table so that the interruption of one tracing operation for another does not require interchanging of the drafts. For this feature to be possible, the apparatus usually in some way must be adjusted for the change of position of the draft on the table. To do this requires major adjustments bet-Ween the tracer mechanism and the copying tool and involves expensive and complex structures.

The invention, therefore, contemplates apparatus of the preceding character that is suited for copying master drafts attached to any part of a `draft table. More particularly, the invention affords an adjustable workpiece support that permits the workpiece to be positioned on any part thereof so as to correspond to the `disposition of the master draft on the dra-ft table. Additionally, by the arrangement, the disposition of the tool support relative to the workpiece affords further support for the workpiece.

rI'he foregoing and other objects and advantages of the 9 invention will be apparent from the following description and the accompanying drawings in which:

FIGURE 1 is a perspective view of a reproducing apparatus demonstrating the principles of the invention;

FIGURE 2 is a diagram of a pressure uid system -or the apparatus;

FIGURE 3 is 4a diagrammatic illustration `of the apparatus optical system;

FIGURE 4 is a View of the reproducing operation as observed ion a TV viewer;

FIGURES 4a, 4b, 4c, and 4d are diagrammatic showings illustrating different operating phases oi a tracer mechanism for the apparatus;

FIGURES 5, 6, 7, and 8 are diagrams of circuits employed by the tracer mechanism;

FIGURES 9 and 9a are block diagrams of the apparatus control system;

FIGURE 10 is a rview partly schematic of a chip re- Inovai rsystem for the apparatus;

FIGURES 11 and 12 are front and side views, respectively, yof :a workpiece supp-ort employed by the apparatus;

FIGURES 13 and 13a are sectional views orf the Workpiece support taken along line 13-13 of FIGURE 1l;

FIGURE 14 is a sectional view of the workpiece support taken along line 14-14 of FIGURE 1l;

FIGURE 15 is a view of ya clamp yfor the workpiece support looking in the direction of arrows 15-15 in FIGURE 14;

FIGURE 16 is a sectional view of a double clamp for the workpiece support taken along line 16-16 of FIG- URE 11; and

FIGURE l7 is a View of the double clamp looking in the direction of arrows 17-17 in FIGURE 16.

GENERAL ARRANGEMENT Referring to FIGURE 1 in detail, the reproducing apparatus depicted has horizontal guideways 10 suitably supported on a lbase (not shown) or the equivalent. A table 12 is adapted to slide along the horizontal guideways 10 and has formed integral therewith, or iixedly positioned thereon, ian upright stand 14. The upright stand 14 cooperates with the table 12 to maintain vertical guideways 16 properly aligned so as to permit vertical up and down movement of a tool support 18 slidably joined to the vertical guideways 16. The tool support 18 has mounted thereon a tool drive motor 20 that through a belt 22 revolves a spindle 24 to which a copying or cutting tool 26 is secured adjacent a workpiece or template 28. An adjustable support for the workpiece 23 will be described in detail subsequently under the heading Workpiece Support. Other modes of ldriving the copying tool 26 may be employed as demanded by particular applications. Also, the versatility of the apparatus is increased if provision is made for revolving the copying tool at diierent speeds :within some select range.

To maneuver the cuttingtool 26- rel'ative to the workpiece 28, two similar drive trains `are employed, one a horizontal drive train denoted generally at 50 and the other a vertical drive train shown at 52. The horizontal ,drive train 5? includes ya drive motor 54, a gear box 56, and a drive screw 5S, whereas the vertical drive train 52 consists of a drive motor 60, a gear box 62, and a drive screw 64. Drive in each train proceeds from the respective drive motor through the gear box and to the drive screw. Each gear box is appropriately arranged to provide the required drive direction change at a desired drive ratio, which may be altered if wanted. From the drive screws 58 and 64 the rotation thereof is transferred in any suitable way, eg., stationary nuts (not shown) attached both to the table 12 and the tool support 18. Hence, with only the horiozntal drive train S0 eiective, the cutting tool 26 will be moved in la horizontal plane corresponding to that of the table 12. Similarly, with only the vertical drive train 52 effective, movement of the cutting tool 26 coincides with the ymovement of the tool support 18 along the .guideway 16.

Preferably, both the horizontal and vertical drive motors 54 and 6% are operated =by fluid pressure delivered thereto under the control of horizontal and vertical duid pressure control units 66 and 68. By utilizing liuid pressure operated motors, resp-onse is instantaneous and the tiuid has an inherent ability to absorb ldrive line shocks such that together smooth responsive operation is obtained. Both of the fluid pressure control units 66 and 68 are of the character employing force motors and servo valves, the function of which is well-known.

Because the two control units 66 and 68 are identical, and because each is of well-known construction, only one, that for the horizontal drive train 50, will be somewhat brieiiy described. As demonstrated in FIGURE 2, a servo valve, designated Vgenerally at 70 and formed with Ia series of spaced lands 72, 74, 76, and 78, is slidably positioned within a bore in a valve body 80. Centering springs 32 and 84 act on opposite ends of the servo valve 7 t) and maintain the yservo valve 7) in the depicted center position in the absence of any force except the spring bias. When in this center position, lands '72 and '74 and lands '76 and 7S respectively interrupt communication between restricted exhaust ports S6 :and 88 and motor inlets 90 and 92. Each of the exhaust ports 86 and SS-is slightly restricted so as to improve operational responsiveness@ With lboth of the exhaust ports 86 and 88 cut off or out of communication with the moto-r inlets 9) and 92, fluid pressure in a main supply line 94 delivered thereto by an appropriate pump 96 at a pressure determined by a conventional pressure regulating valve 97, is supplied to both motor inlets 91? and 92.

A suitable solenoid operated valve 9S in line 94 between the pump 96 and the regulating vaive 97 interrupts communication therebetween whenever the solenoid winding therefor is deenergized. The function and purpose of this valve 98 wil-l Ibecome apparent.

With this arrangement, when the 4servo valve '70 is in the center position, the drive motor 54 is ineiective, but when the servo valve 70 is maneuvered in either direction, the pressure supply to one of the motor inlets 99 or 92 will lbe reduced or enti-rely cut oft with the result that the pressure being delivered to one or the other of the motor inlets and 92 will dominate and the motor 54 Will be rotated thereby in the corresponding direction. The inlet to the motor 54 with the reduced or cut 01T pressure will be relieved thnough Aone or the other of the exhaust ports 86 and 88.

The production of the variable pressures for maneuvering the servo valve 70 is under the control of a force motor denoted generally at 100. For this control the motor `100 employs a reed valve 102 pivoted at 104 and arranged so as to enter the valve body 80l as viewed. The point of entry of the reed valve 102 into the valve body 80 may be sealed by a seal element 106 or may be left open if drainage to sump is possible. Energization of one or the other of opposite relays 108 and '110 respectively by regulating signal voltages respectively from an X-axis summing circuit 1112 and an X-axis servo arnplitier -114 and a Y-axis summing circuit 1116 and a Y- axis servo ampliier 1'1-8 will cause the reed valve 102 to pivot about the axis determined by the pivot point 104 and in so doing the end entering the valve body 80 will restrict one or the other of adjacent control orifices l and 122 thereby altering the pressure of the fluid acting on the opposite ends of the servo valve 70. The supply of fluid pressure for this purpose is delivered by a branch 124 of the supply line 94 through opposite supply oriices 126 and 128 to the end areas of the servo valve 70. The supply oriiices 126 and 1,218 create a pressure differential between the branch 1124 and the chambers at opposite ends of the servo valve 70. Without these orifices 126` and 1-28, control would not be possible since fluid pressure would be relieved via an exhaust chamber 130 through either of the control orifices 120 and 122 or both.

If the reed valve 162 is in the illustrated center position, the fluid pressure acting on opposite ends of the servo valve 70 will be relieved through the exhaust chamber 130. However, if the reed valve 102 abuts or partially restricts one of the control orifices, e.g., control orifice 1'20, the pressure upstream thereof will build up. This pressure, when adequate, will move the servo valve 711 to the light reducing or cutting off the supply to fluid pressure to the motor inlet 90 while increasing the supply of Huid pressure to the opopsite motor inlet 92. Accordingly, the horizontal drive motor 54 will revolve in a corresponding direction. Meanwhile, the motor inlet 911 will be partially or completely relieved through eX- haust port 86. The same events will occur in reverse if the reed valve 162 restricts control orifice 122, i.e., the servo valve 7i) now :will be moved to the left so that the pressure to the motor inlet 90 will dominate while that in the motor inlet 92 is partially or completely relieved via exhaust port '8%. With this latter situation, the horizontal drive motor 54 will reverse in direction of rotation.

`On the side of the apparatus opposite the workpiece 23, a master draft table 132 is pivotally joined to some fixture such as the apparatus base and has attached thereto a master draft 134, which may be a print, drawing, or the equivalent having a contour line as line 136 to be traced. The pivotal movement of the master draft table 132 permits the table to be positioned in a horizontal plane when the master draft y134 is attached. Then the table 132 may be moved to the demonstrated vertical position and locked in place. A number of lamps 138 are positioned in the vicinity of the master draft 134 so as to light up the part of the contour line 136 to be traced. These lamps 138 may be secured to the table `132 and/ or arranged for movement with the tool support 18. Additional lamps may be employed as needed.

An optical system denoted generally at 1141i and displayed schematically in FIGURE 3, is so arranged as to provide dual images of the portion (enclosed by a circle 141) of the contour line 136 being traced. This is effected by splitting the image in a known way transferred from a lens 142 to `a split image lens i144. One of the images is transferred ythrough an upright tower y146 (FIG- UR-E l) carried by the tool supoprt 18 and projected at a magnification determined by magnifying lens 148 and 115) on a frosted glass screen 152 at the top of the tower 146. The other image proceeds through an opening 154 at the base of the tower 146 `and is correlated with a reticle 156 simulating the copying tool 26 and an image producer as TV camera l158. Both the reticle 156 and the TV camera i153 are accurately positioned on a shelf 1611 scoured to the tool support 1-8, so that an electronic image is developed thereby showing the outline of the reticle 156 superimposed on the contour line image. This enables an accurate reproduction of the disposition of the tool 26 relative to the contour line `136 being copied to be obtained, e.g., as viewed in FIGURE 4, and is accomplished in a Well-known manner by coordinating the focal lengths of the TV camera 1518 and the splitv image lens 144.

The image projected onto the frosted screen '152 is utilized by a tracer mechanism denoted generally at 1162 for the automatic aspect of the apparatus, whereas the image to the TV camera 158 is through a suitable closed system projected onto the screen of a TV viewer e164 remotely positioned from the apparatus at an openators station as control panel 1166 containing various manually operated controls. This permits the operators station to be in a room dilferent from the apparatus, affords a bet` ter picture of the cutting action, and protects the operators from the dangers inherent in any machining process.

6 Tracer Mechanism The tracer mechanism 162 develops, as will become apparent, when off-course or orf-line relative to a contour iline, error signals that are used in operating the control units 66 and 68. As best shown by FIGURE 1, a bracket i168 is suitably mounted both for movement with the tool support :1 8 and for revolvable movement re-lative thereto. The disposition of the bracket 16S relative to the optical tower 1'46 permits a photosensitive device denoted generally at 170 to be located above the screen `11:12. The photosensitive device i170 is made up of a photohead 172 that ifs movable along a dnive arm =174 for a reason to be explained. The photohead 1172 carries a set of on-line or on-course photocells 1176, a set of off-line or olf-course photocells 178, and two sets of steering or guidance photocells and 1182 all arranged when an on-course path is being followed as illustrated in IFIGURE 4.

The operation of the individual photocells is wellknown, and of course, the relationships may be altered to iit requirements of different applications. Briefly, when a photocell is arranged in series with a voltage source and a load, dark objects cause the photocell to function somewhat as a high resistance; therefore, all of the voltage drop or substantially all of the voltage drop occurs across the photocell and none happens across the load. With a light object, the resistance ofthe photocell to current flow is less, and hence, the voltage drop is not as great across the individual photocells,

Since it is desirable to use different size cutting tools and also because cutting tools wear, the movement of the photohead 172 mentioned will compensate for these different size cutting tools. To explain, it must be kept in mind that the contour line 136 appearing on the screen 152 of the tower 146 is considerably magnified, e.g., 2O to l. Therefore, the radius about which the photohead 1'72 revolves, will have to be a predetermined amount greater than the actual radius of a circular cutting tool. For instance, assume that a contour line with the configuration depicted in FIGURE 4d is to be cut. the tool radius is greater than the radius of the curve, the .line cannot be reproduced unless the tool diameter is reduced to an appropriate size. The same applies to the radiuson which the photohead 172 operates, for the photohead radius must be reduced in order to also maneuver around the 20-1 magnified curve. This is done by sliding the photohead 172 back and forth on the drive arm 174. To obtain accuracy, gauges or the equivalent may be positioned along the drive arm 174 so as to permit very accurate positioning.

Referring to FIGURE 4, which represents the picture seen on the TV viewer 164 when on-line or on-course operation is occurring, the relative positions of the photocells have been shown for explanation purposes only. Actually they will not appear on the screen of the TV viewer 164. The outputs of the various sets of photocells indicate their disposition relative to the contour line 136, and it is these error signals that are utilized, as will become evident, for reproducing the contour line 136 on the workpiece 28. l

The use of two sets of steering photocells 180 and 182 in maintaining parallel alignment of the photohead 172 with respect to the contour line 136 enhances accuracy since with just one set it can be seen that the contour line 136 may be positioned parallel to the direction of movement of this single set only with respect to the set whereas other parts of the photohead 172 may be out of parallel alignment therewith, i.e., pursuing a different course. The diagonally opposite photocells of these steering sets 180 and 182 are so connected that their outputs when a misalignment exists produce a signal of a polarity and a magnitude determined by the direction and amount of error. For example, as seen in FIGURE 4a, the bottom or lower photocell 180" of the set 180 and the top photocell 182 of the set 182 may be both positioned over the same line 136. An error signal will be developed such Obviously, ifV

that the photohead 172, assuming to be the rotational aXis thereof, will have to be revolved counterclockwise to attain the FIGURE 4 parallel alignment and these two photocells 180 and 182 being connected with their outputs joined will provide an error signal voltage of one polarity, e.g., positive, and of a magnitude equivalent to the amount the photohead 172 must be revolved in a counterclockwise direction. On the other hand, if the misalignment is such that the top photocell 180' of the set 180 and the lower photocell 182" of the set 182 are positioned above the contour line 136", an error signal voltage will be producedrof an opposite polarity, negative if the other is positive, and of a magnitude that willcause the photohead 172 to be revolved in a clockwise direction until the photocells are properly aligned with the contour line 136" as in FGURE 4.

With these two sets of steering photocells 180 and 182 arranged to have the outputs of the diagonally opposite photocells joined together, no error signal will be developed as long as the two sets of photocells 180 and 182 are parallel to the contour line 136,` but this does not mean that the photocells for each set must straddle the line. On the contrary, they may be considerably displaced from the contour line 136 while following a parallel course and no error signal will be developed. Because of this, the on-line set of photocells 176 is incorporated in the photosensitive device 178 for maintaining the tool 26 normal to the contour line 136. These two on-line photocells 176 if on-course straddle the contour line 136 and no error signal is produced, but if there is a slight lateral deviation, although proper parallel alignment exists relative to the two sets of steering photocells 180 and 182, an error signal will be developed of a polarity determined by the side of the contour line 136 that the tool 26 has moved off-course, and of a magnitude corresponding to the off-course distance.

The off-line set of photocells 178 is intended to cause vthe apparatus to be stopped when the off-course error exceeds some predetermined amount. Normally, as viewed in FlGURE 4 and as will be explained, when on-course the ofi-line photocells 178 will produce a signal since the outputs therefrom will not be balanced with one of the photocells positioned over the contour line 136.

The error signals from the on-line set of photocells 176, and the off-line set of photocells 178 and the two sets of steering photocells 180 and 182 are transferred respectively through appropriate preamplifiers 184, 186, and 188. The outputs of these preamplifiers 184, 186, and 188 are in turn joined to a brush and slip ring arrangement displayed at 19t) and the various error signals are then picked off in this manner. By having the preampllfiers on the input side of the slip ring arrangement 190, much of the noise from the slip rings is not induced into the control system, and therefore, the arrangement otfers an advantage in this respect.

The number of photocells in each grouping as sets 18), 182, 178 and 176 and their capacity will, of course, be determined by the application of the apparatus and accordingly will influence the strength ofany signals developed. With a strong signal, the inuence on the operation of the tracer mechanism 162 from external sources, e.g., intersecting lines, is greatly reduced.

Because there may be different lighting conditions and because the reflectivity of different master drafts, one may be dark and the other relatively light, provision 1s made for balancing the outputs from the photocells in each of the several sets. This is necessary because two otherwise similar photocells will generally not, under identical conditions, have the same output and the difference in output would produce an error signal in the system. The balancing of the outputs is accomplished by a lighting and reflectivity compensator shown generally at 192 in FIGURE 9. A

The outputs of each related set of photocells may be balanced in the same manner, eg., a Wheatstone bridge;

hence, only the one shown in FIGURE 5 will be described. The others will be exactly'the same and the arrangement may be applied as will be understood by those versed in the art. As seen in FlGURE 5, the outputs of the on-line set of photocells 176 are connected to the input of the preampliiier 184. If both of the photocells 176 are positioned over an area formed of material with the same degree of reectivity `and provided with the same amount of light, the bridge should be balanced. Since the outputs generally will not lbe balanced, then a variable resistor shown at 194 is installed in the circuit therefor and arranged both in series between a grounded resistor 196 and `a resistor 198 in parallel with a voltage source for the photocells 176. An adjustable arm 200 for the variable resistor 194 extends to the photocell anodes both of which are joined to the input of the preamplifier 184, and has a suitable connection with an ammeter 284 or the equivalent communicating with the output of the preamplifier 18d. If the outputs from the two photocells are in balance, the needle of the ammeter 204 will be centered. If not, a knob 206 may be ma neuvered so as to alter the setting of the adjustable arm 280 and `cause the needle to be returned to the centered position. The variable resistor 194 therefore functions to establish a reference voltage by causing more or less current iiow to the output circuit of the on-line set of photocells 176.

To obtain different polarites, ya reference voltage, e.g., volts is selected for maintaining the needle of the ammeter 284 centered. Then, if the output is less than -85 volts, an error signal of one polarity will he produced and if the error signal is greater than the -85 volts, an error signal of an opposite polarity will result. Hence, the polarity will determine on which side of the contour line 136 the photohead 162 has moved and provide an error signal of the proper magnitude and polarity for making the necessary correction.

As mentioned, the off-line set of photocells 178 cause operation of the apparatus to be interrupted if the offcourse error is too great. The o-line error signal developed when the off-course error has not exceeded the prescribed limits is amplified by a suitable amplifier 288 and this amplified error signal, as seen in FIGURE 9, causes a relay 210 to be energized with the result that contacts 214m are normally open and contacts 21011 are normally closed. If the off-course error is too great, then the off-line error signal is substantially reduced so that the relay 210 is deenergized. As a result, contacts 210:1 will be closed Iand contacts -21b will be opened. Contacts 21011 control a circuit for a lamp 216, which will be stationed on the operators control panel 166Y so as to light up when off-course any prescribed amount. By opening the contacts 218i), the circuit to the solenoid operated valve 98 will be interrupted or opened, and hence, the solenoid winding will be deenergized so as to cause the valve 98 to interrupt the supply of fluid pressure to the motors S4 and 60. This stops automatic operation until the tool 26 is brought back on course in a Way to be explained.

The steering error signals are amplified by a suitable D.C. amplifier 218 and then are transferred through a manual-automatic switching circuit shown at 220 in FIG- URE 9a. In this switching circuit 220 a pair of contacts 222e (seen in FIGURE 6), which are closed during automatic operation by a relay 222 seen in FGURE 8, are closed while related contacts 226a normally closed during manual oper-ation are opened by a relay 226. Assuming that the various contacts are opened and closed for automatic operation, the Icircuit in FIGURE 6, including parallel resistors 230 and 232, from the D.C amplifier 218 to a magnetic amplifier 234 of appropriate construction will be completed. The operation of the magnetic amplifier 234 is well-known and in this embodiment the magnetic amplifier 234 is joined to a Scott two-phase transformer 236 in such a manner that one phase operates a two-phase motor 238 directly, whereas the other phase is subject to the control of the D.C. steering error signal. The polarity and magnitude of the DC. steering error signal will determine the direction and speed of rotation of the two-phase motor 238.

Associated with the two-phase motor 238 and revolvable thereby is a D.C. tachometer generator 24o arranged to produce a feedback voltage corresponding to the speed of rotation of the two-phase motor 238. Also, this feedback voltage may be altered by kany suitable adjustment, e.g., by variable resistors in the manner to be explained with respect to the adjustment of the feedback signal voltages supplied the X- and Y-axis summing circuits 112 and 116. This feedback voltage is utilized by the magnetic `amplifier 234 to alter the influence of the error signals such that stability of operation results, i.e., minor speed iluctuations do not influence the operation nor does so-called overshooting occur; for otherwise, the twophase motor 23S with a large magnitude error signal if not reduced by the feedback voltage would be caused to revolve too fast. `If revolving too fast, the motor 23S tends to pass the desired point.

The two-phase automatic guidance or steering motor 238, as can be observed both in FIGURES 1 and 2, revolves a shaft 242 and this shaft in turn causes the drive arm 174 to turn the bracket 168, and accordingly the photohead 172, clockwise or counterclockwise as required and as explained with respect to FIGURE 4a. A speed reducing gear box 244 stationed on the output side of the two-phase motor 238 offers a speed reduction determined by the application. On the output side of the gear box 244 a suitable slip clutch 245 is positioned and set to slip at a predetermined torque so as to protect the gear box 244 from damage in case the bracket 168, the photohead 172, or some other part of the drive train offers excessive resistance suiiicient to damage the gear box 244. Next in order, continuing downwardly from the slip clutch 245 and positioned on the shaft -242 are a synchro 24S, and two impedances, as automatic steering sine-cosine potentiometer 2549 and on-line sine-cosine t potentiometer 252, the functions and purposes of which will be hereinafter explained.

The oli-course error signal is amplified by a diierential amplifier 254, FIGURE 9, which may be a conventional amplifier with a phase inverter circuit or the equivalent, correlated so that there are two outputs from the ampliiier 254 equal in magnitude but opposite in polarity. The reason for the dual outputs of opposite polarity can be best understood by reference to FIGURE 7 and the demonstrated arrangement of the on-line sine-cosine potentiometer 252. As shown, the potentiometer 252 includes a stationary winding 256 connected to the output lines 25S and 26) from the dierential amplier 254 and are provided with ground connections at 262 and 264. An X-axis contact arm 266 and a Y-axis contact arm 268, each disposed 90 apart and each revolvable by the shaft 242, coact with the winding 256 to produce a control voltage determined by the position of the shaft 242 and the magnitude of the input oit-course error signal. The X- axis arm 266 and the Y-axis arm 26S are connected respectively through resistors 270 and 272 and through the manual-automatic switching circuit 220 to the X- and Y- axis summing circuits 112 and 116. The switching circuit 220 includes automatic yand manual X-axis contacts 274a and 274!) and automatic and manual Y-axis contacts 274C and 274:1?, all operated by a relay 274, illustrated in FIG- URE 8.

As can be seen from FIGURE 7, if automatic operation is established, the automatic X- and Y-axis contacts 274a and 274C are closed while the manual X- and Y-axis contacts 274-b and 2'74d are open. lf the reverse is true, i.e., manual operation is wanted, the manual X- and Y-axis contacts 274b and 274d connect the lines extending to the summing circuits to ground and the outputs from the potentiometer 252 ydo not influence the 10 operation of the X- and Y-axis summing circuits 112 and 1116.

To further understand the operation of the on-line sine-cosine potentiometer 252, the position depicted in FIGURE 7 will iirst be considered. As can be observed, the X-axis arm 26 is grounded at 262, whereas the Y-axis arm 268 is in contact with the winding 256 at the output line 26th There will be no X-axis signal With this disposition of the potentiometer 252, but there will b e a maximum Y-axis signal of a polarity determined by the output line 261i. To explain this change of polarity, reference is made again to FIGURE 4d where the conventional X- and Y-axes are shown and the contour line is displayed with relation thereto. Assuming initially that the on-line photocells 176 are in the top position so that a negative output is ydeveloped due to the off-course error, then if this oil-course error is maintained and the set of photocells 176 continue around the curve in the direction of the arrow, ie., in a counterclookwise direction, the disposition of the photocells 176 relative to the line will be that viewed below the X-axis. Under these conditions the photohead 172 will have been rotated 180. When the photocells 175 Were above the X-axis, to correct the oni-course error required that the photohead 172 be laterally displaced downwardly in the direction or" the arrow and the correction was determined by a negative signal. Now, with the photocell 176 in the position below the X-axis, a correction will have to be made by moving the photohead 172 upwardly in the direction of the arrow if the two photocells 176 are to straddle the line in the oncourse position. But, the errorsignal is still negative and this negative signal causes opposite movement of the photohead 172. However, by revolving the photohead 172 180, the Y-axis arm 268 will .contact a point opposite the positive output 258 and the proper correction can be made. Therefore, by having both a positive and negative signal of the same magnitude produ-ced from a single error signal, the proper corrections can be made as the photohead 172 revolves and this situation explained relative to FIGURE 4d does not present a problem.

So as to aid in understanding the other sine-cosine potentiometers employed in the system as well as the on-line potentiometer 252, attention is directed to FIG- URE 4c where the arms 266 and 268 have been displaced so that each will have a voltage applied thereto. The Y-axis controlledsignal will be positive and the X-axis control signal will be negative in these positions. The magnitudes of each when vectorially correlated on the FIGURE 4b conventional diagram commonly used for solution of circular trigonometric functions will result, e.g., in an angle of 30 as indicated. The resultant of the negative X value and the positive Y value will require movement equivalent to the value R and in the direction thereof for the photocells 176 to be positioned straddle the line 136 shown with relation thereto. The resultant R is of course the vectorial sum of the X and Y Values and it is these X and Y values that cause the drive motors 54 and 66* to be operated so as to result in movement of the tool 26 corresponding in direction and magnitude to the resultant R.

The automatic steering sine-cosine potentiometer 259 functions very similarly tothe on-line potentiometer 252 v and includes a stationary winding 284, that is joined to input lines 2&6 and 28.8 and that has yground connections at 290v and 292. The input lines 226 and 2nd provide signal voltages of the denoted polarity but of equal magnitudes corresponding to the desired speed of operation as will become evident. An X-axis contact arm 2194- and a Y-axis contact arm 296 are connected respectively through resistors 293 and 360 and through the manual-automatic switching circuit 22o to the X- and Y-axis summing circuits 112 and 116. As with the on-lfine potentiometer 252, automatic and manualX-axis contacts 30261. and 302k and automatic and manual Y- axis contacts 302e and Sil-2d are all operated by a relay 302 such that when automaticoperation is selected, the automatic X- and Y-aXis contacts 302a and 302e are closed and normally closed manual X- and Y-aXis contacts 30211 and 302d are opened for reasons to become apparent.

As will be noted, the X-axis arm 294 for the automatic steering potentiometer 250 is 90 displaced from the X- axfis arm 266 for the on-line potentiometer 252. The same is also true for the Y-axis arms. The explanation for this is obvious whenV again considering FIGURE 4b, for as can be observed there, it is assumed that the photohead 172 is proceeding upwardly along the line 136 and in parallel alignment therewith but o-course, any correction made to bring the tool 26 back on `course will be at 90 to the line 136 or normal with respect thereto.

Additionally, assuming that the slope of the line to be traced is at an angle of 60, as the line S in FIG- URE 4b, the steering control signals for following the slope of 60 will have positive X- and Y-axis values determined respectively by the cosine and sine functions of the A60" angle. The sum of these two X- and Y-axes values will always result in the same value, when summed vectorially. Hence, if the speed desired of the tool 26 relative to the workpiece 28 is l0 inches per minute, regardless of the slope of the line S, the speed will always be l() inches per minute, a desirable feature since constant speed is wanted for eicient operation.

Because, as mentioned, the arms of the two potentiometers 250 and 252 are linked together 90 apart, the X-axis value for determining the on-line control signal with respect to line S will be determined by the sine function of the 60" angle, whereas the Y-axis value will be determined by the cosine VJfunction of the 60 angle. This is apparent from the diagram in FIGURE 4b since these values would produce a line with a slope equivalent to that of the line R.

The speed signal voltages supplied to the input lines 286 and 288 on the automatic steering sine-cosine potentiometer 250 are selected manually at the operators panel 166 by maneuvering a dial 312. rlfhis dial 312 is linked or otherwise secured to the also linked contact arms 314 and 316 as observed in FIGURE 7 and these arms 314 and 316 in turn coact respectively with speed control potentiometers 318 and 320. The speed control potentiometer 320 is connected to a negative voltage source through a fixed resistor 322 and a variable resistor 324 whereas speed control potentiometer 3118 is connected to a positive voltage source and through a fixed resistor 326 and a variable resistor 32S. The relationship of these resistors will produce output voltages of opposite polarity but of equal magnitude, the magnitude being determined by the speed desired. If a greater speed is wanted, then the potentiometer arms 314 and 3'16Vare positioned so that the voltage drop is less and when less speed is required, the arms 314 and 316 are positioned so that the voltage drop across the potentiometer is increased. Consequently, when these potentiometers 313 and 320 are combined with steering potentiometer 250, the tool 26 is caused to be maneuvered in the `direction determined by the position of the arms 294 and 296 for the potentiometer 250 at a speed determined by the speed control potentiometers 318 and 320.

As seen in FIGURE 9a, an appropriate limitswitch control 330 is actuated by the movements of the speed control dial 312. This limit switch control 330 communicates with the solenoid operated valve 98 and functions when the speed control dial 312 is turned to the valve 9S to be deenergized thereby interrupting the sup- 12 ply of fluid pressure to the motors 54 and 60. Thus, the limit switch control 330 precludes the possibility of tool creeping movement when the speed control 312 is in the Ofi position.

Positioned above the speed control dial 312 in FIGURE 9a is the manual steering control dial 332 also shown in FIGURE .-1 on the operators panel 166 to the rig-ht of the speed control dial 312. The manual steering control 332 revolves a manual guidance or steering Ishaft 334, which in sequence operates ia cam limit switch 336, a synchro 338, and a manual steering sine-cosine potentiometer 340. Also mounted on the same shaft 334 is a slip clutch 342, a speed reduction gear Ibox 344, and a motor 346. 'Ihe gear box 344 and the slip clutch 342 perform the same functions as the gear box 244 and the slip .clutch 245 cn automatic steering shaft 242.

The manual steer-ing sine-cosine potentiometer V340 (FIGURE 7) is similar to the automatic steering potentiometer 250 and includes Ia winding 348 connected respectively to branches 350 and 352 `of input lines 288 and 286 from the speed control potentiometers 318 and 320 and grounded at 354 and 356. An X-axis Contact arm 358' extend-s to the manual-automatic switching circuit 220 through a resistor 360, and a Y-axis contact arm 362 extends to the same circuit 220 through a resistor 364. The X-axis and Y-axis arms 358 and 362 are maneuvered by the shaft 334 and as with the potentiometers 250 and 252, the arms thereof are displaced apart. When the manual X- and Y-axis contacts 302b and 30211 are in the normally closed position, steering may =be accomplished in the same manner as that done by che two-.phase motor 238 in maneuvering the photohead 172.

The cam limit switch 336y is operated by appropriate switch operators (not shown) in turn actuated when the table 10 and the tool support 18 attain substantially all of the penm-it-ted travel in their respective directions. For instance, if .the tool support 18 has moved up or down the maximum allowed extent, the corresponding switch operator will actuate the cam limit switch 336 and cause the solenoid Winding for the solenoid openated valve 98 to be deenergized. As a result, the fluid pressure supply to the motors 54 and 60 is interrupted land accordingly travels of the table 10 and tool support 18 .are stopped before damage to the apparatus can occur.

' Both of the summing circuits '112 and 116 are similar, and hence, it will be only necessary to describe one. Consideritng then the X-axis summing circuit 112, FIGURE 7, this circuit has an X-'axis steering control signal voltage input 366 :from both the automatic and the manual steering potentiometers 250 and 340, an X-axis olf-.course control signal voltage input 368 from the on-line potentiometer 252, an oscillating signal voltage input 370 joined to any suitable dither oscillator 372 through a capacitor 374, and a feedback signal voltage input 376.

'llhe dither oscillator 37 2 gives a continuously oscillating effect to the summed signal voltage so as to keep the components orf Ithe control 'units 66 and 68, particularly the force motors and servo valves alive or continuously oscillating as well as the other elements of the control system. This gives instantaneous response by removing the influence of static Ifriction. The capacitor 374 is utilized in conjunction with the dither oscillator 372 so as to eliminate the influence of the summing circuit on the dit-her oscillator 372.

To obtain the feedback signal voltage, an X-axis D.C. tach-ometer generator 378 is arranged as Ademonstrated in FIGURE l for rotation with the motor 5'4 and thus produces a feedback signal voltage that corresponds to the speed lof the screw 58. This feedback signal voltage is adjusted to la desired value Iby variable resistor 380 (see FIGURE 7) situated in the input 376 yand is utilized to prevent ovenshooting as previously mentioned, as well as for removal of the iniiuence of minor speed fluctuations on the control units 66 and 68; A grounded capacitor 382 .provides some filtering and also aids in removing liuctua- 13 tions from the system. The impedances 384, 386, 388i, and 390 will normally lbe resistors unless the signal voltages are to Ybe modified in some other Way.

All of the various signal voltages are added algebraically lby lthe circuit 112 and the sum is applied to a gain potentiometer 392 positioned at the input tothe ampliiier 114. Hence, an amplied regulating signal voltage is afforded for operating Ithe control unit 66.

'IThe Y-axis summing circuit 116 and the components thereof have been assigned the same numerals as the X- axis summing circuit 112 but with primes added thereto. For instance, the Yeaxis steering co-ntrol signal voltage input is assigned the numeral 366', the Y-axis off-course contr-ol signal voltage 4input the numeral 368', and the Y-aXis D C. tachometer `generator the number 378.

The 4feedback input 376 has installed therein grounded X-axis contacts 394a, whereas the Y-aXis feedback sig-nal voltage input 376' Ihas grounded Y-axis contacts 39'4-b. Both of these contacts 394a and 394b are operated by a rel-ay 394- in turn under the control of a rapid traverse switch 398 displayed in FIGURE 8 and which may be made accessible to the operator, if desired, by placing within the control panel 166. When this switch 398 is actuated, relay 394 is energized and the contacts 394e and 394b are closed, thus shorting the feedback signal voltages :to ground .and eliminating the iniiuence thereof on the summing circuits 112 yand 116. As a consequence, the regulating signal voltage developed will be of a greater magnitude and the motors 54- and 60 will be operated at a faster speed to give rapid movement of :the tool 26 att certain times for instance when it is 'desired to move the tool 26 quickly to the line to be reproduced.

As will lbe explained during the operational summary, both manual and automatic operation are possible, therefore, it is necessary to synchronize the notation of the manual steering shaft 334 with 4than: of the [automatic steering shaft 242. There `are many Iways to laccomplish this as those versed in the art 'will understand. However, it is preferred that this be accomplished electrically. For this purpose the synohros 24S and 33% mentioned previously are employed.

Both of the synchros 248 and 338 may be of any known constitue-tion such as shown schematically in FIGURE 6. As there depicted, the manual steering shaft synchno 33S is disposed so as to lfuncton as the transmitter and therefore has a rotor winding 400 revolvalble by the shaft 334. Stator coils 492 arranged in va Y configuration are positioned adjacent the rotor winding 400i and the rotor winding 400 is furnished with an A.C. voltage through slip rings or the equivalent from an extennal source. The automatic steering shaft synchro 248 accordingly will function as a receiver and has stator coils 404, also aligned in a Y, connected to the manual synchro stator coils 402. A rotor winding 466 is revolvable with the automat-ic steering shaft 242. -If preferred, the stator coils may be revolved with the shafts land the rotor windings held stationary.

If the shaft 242 is out of synchronism with the shaft 334, `an A.C. error signal voltage will be developed in the automatic synchro rotor winding 4% indicating the amount that the sha-ft 242 is out of angular alignment with the shaft 334. To utilize this A.-C. error signal voltage, it is necessary to develop a D.C. equivalent, and hence, rotor winding 4% is joined to a demodulator 4%, which develops from the A C. error signal voltage a D.C. equivalent error signal voltage. This DC. signal voltage is increased to a desired level by an amplifier 41% and if manual operation is effective, this DC. error signal will be applied to the magnetic amplifier 234 through contacts 22.5a and cause, in the foregoing described manner, the two-phase motor 233 to be rotated sufficiently to bring the shaft 242 back into synchronisrn with the manual steering shaft 334.

if, on the other hand, automatic operation is selected, the contacts 226a will be opened and contacts 226]; closed by relay 226. This completes a circuit, similar to that between the amplier 218 and the magnetic amplifier 234, between the amplifier 410` and a magnetic amplifier 414. This latter circuit also includes parallel esistors 416 and 418. Hence, a DC. error signal voltage developed in this manner will control the magnetic amplifier 414 in the same way as the magnetic amplifier 234 is controlled, i.e., the magnetic amplifier 414 will be connected toI the same transformer 236 or a similar one with one phase thereof joined directly to the two-phase lmotor 345 while the other phase is controlled'by this D.C. error signal voltage, suc'h that the two-phase -servo motor 346 is caused to revolve the shat 334 suiciently to bring the two shafts 242 and 334 into synchronism. The motor 346 and magnetic amplifier 414 also have a DC. tachometer generator 420 and an adjustment to furnish a feedback voltage for the ycarne reason mentioned with respect to the tachometer generator 24?.

The manual-automatic switching circuit 220 -is controlled by a manual-automatic button 422 at the operators control panel 166 and this button 422 operates a manual-automatic switch 424 shown in FIGURE 8. The switch A424, when closed, completes a circuit extending from a power supply 426 to relays 274 and 332, 222 and 226. With the switch 424 closed then, automatic operation will take place since all of the associated normally closed contacts are open as contacts 274b, 2746i, 362i?, 302e', and 226/1. Those contacts normally open, as contacts StiZa, 3il2c, 27451, 274e, 22617, and 222e, will be closed, thus preparing the system for automatic control as `will be explained in the operational summary.

Because it may be necessary to maintain the tracing mechanism 142 along a certain course when an intersection between lines is encountered, a freeze button 428 is placed also at the operators control panel 166 -for this function and operates a freeze switch 431i illustrated in FEGURE 8. With the 4freeze switch 430 in the depicted position, automatic control is possible since the relays 362, 222, and 22o can be energized when the manualautomatic switch 424 is c-losed. Assuming that the automatic control sys-tem is effective, by depressing the freeze button 424, the freeze switch 43@ will open and the relays 392, 222, and 226 will return to the position in which the normally closed contacts 3G2b, ilgd, and 22611 controlled thereby are again closed as during manual operation. Specifically, the automatic steering control potentiometer 25h` is rendered ineffective and the manual steering control potentiometer 340 elfective when contacts 39251, 302C are opened and contacts 3l2b, 3620! are closed. The automatic on-line signal potentiometer 252 maintains its status, the relay 274 continuing to hold contacts 274e and 27412 closed, and the contacts `22nd set up the described manual-automatic synchronizing between shaft 334 and 242. This part of the operation will be further explained during the operationalsummary.

Chip Removal System During the cutting operation it is desirable to withdraw the chips removed from the cutting area as quickly as possible. In this way, the overall effectiveness is enhanced since the removed chips are not permitted to interfere with observation of the cutting action or the workpiece surface smoothness and accuracy and additionally the potential safety hazard from chips is eliminated.

ie chip removal is achieved by a pressure system demonstrated in FlGURE l0 and the removed chips are transferred to a remote storage place. As illustrated, the spindle 24 to which the cutting tool 26 is attached, is surrounded by a housing 432 so shaped that an annular chamber 434 is lformed between the spindle 24 and the housing 432. This annular chamber is joined to a chip removal tube 436 that communicates with a vacuum pump 43S. Chips withdrawn then are transferred by the vacuum pump 438 to a storage bin 445i at some posi- .tion away from the apparatus. With this apparatus, when machining the workpiece 28 with a helical iutcd circular cutter, the workpiece 28 is held against the housing 432 and this feature not only aids in the quick Withdrawal of the chips through the flutes of the ycutting tool but also helps maintain the workpiece rigidly supported as will be further explained. Not only are the chips removed, but any dirt or dust also will be withdrawn with this system.

Workpece Support To permit the master draft 134 to be installed on any part of the draft table E32, it is necessary that a suitable holder be furnished for the workpiece 28 such that the workpiece 28 may also be placed in a corresponding part of .the holder. This is because the tracing mechanism 1162 moves with the tool 26 and hence will be tracing in an area of .the draft table "132 that will coincide with the corresponding section of the workpiece 23. The workpiece support ,denoted generally at 441 effects this and includes a iframe 442 `displayed in FIGURES l1 and l2. As viewed in FlGURE ll the frame 442 has upper and lower horizontal g-uideways 444 and 446 and lett and right vertical lguideways 448 and 456, all of proper construction, c g., `:formed as the tubular guideways illustrated in FIGURE l2. The left and right vertical guide- Ways 448 and 450 afford guide tracks both for an upper horizontal column 452 that has lett and right end guide sleeves 454 and 456` embracing the vertical guideways 448 and 450 and a lower horizontal column 458 likewise provided with left and right end guide sleeve 460 and 462 slidably disposed on the left and right vertical guideways 448 and 450. The horizontal .guideways 444 and 446 support both a left vertical column 464 through upper and lower end guide sleeves 466 and 468 and a right vertical column 470 through upper and lower end guide sleeves 472 and 474.

The opposite ends of each of the horizontal columns 452 and 458 are Xed with respect to their respective guideways by vertical guideway clamps 476. One such clamp is depicted in FIGURES, 14 and l5 and employs a' wedge 478 that fits through an opening in the end guide sleeve 462 so as to engage the surface of right vertical guideway 45d. The wedge 478 is pivotally joined to one end of a lever 480, the opposite being pivoted at 482 to the sleeve 462. The lever 486` is actuated by a cam surface 434 on a handle 486` pivoted at 48S on a stud 490 afhxed to the sleeve 462. Consequently, as the handle 486 is pivoted, .the lever 484) is maneuvered so that the wedge 473 is moved into and out of wedging engagement with the guideway 450. The configuration of the cam sunface 484 -is formed so as .to be self-locking, i.e., when the handle 486` is in the locked position and is relieved of manual restraint, thus the cam surface 484 will maintain the wedge 478 in engagement with guideway 45t); As now can be seen, in the locked position of the handle 486, a clamp action on the lguideway 45t) occurs between the wedge 478 and the sleeve 4612, the action being in effect similar to that of a vise.

Referring to FlGURES 11 and 13 and 13a, a horizontal guideway clamp 492 is employed to lock the right vertical column 470 to both the upper and lower horizontal guideways y444 and 446. Clamp 492 includes a handle 494 that is pivoted at 496 to the column 470 and that has an offset crank part 49S with a center at 56d. This oliset crank part is suitably attached to a rod 592 extending the length of the column `470|. At the upper end, the rod 502 is attached to an upper L-shaped lever 564 pivoted to the end guide sleeve `472 at 596. Lever 504 is provided with a shoe portion 508 s-uch that when the lever 504 is revolved clockwise, as viewed in FIGURE 13, the shoe portion 508 will be forced into engagement with the upper horizontal guideway 444. Similarly to clamps 476 the sleeve 472 and the shoe portion 508 will, due to the clamping action, maintain the vertical column 470 stationary at ,the upper end relative to the horizontal guideway 444.

16 In the same way, the rod S02 is pivotally Iattached at the lower end to a lower L-shaped lever 51%) pivoted at 512 to the end guide sleeve 474 and formed lwith a shoe portion 514 engageable with lower horizontal guideway 446.

To release the clamp 492, the handle 494 is moved downwardly, as viewed in FIGURE 13a, to so maneuver the rod 502 that the clamp action at both ends relative to the guideways is relieved. When the handle 494 is moved to the illustrated position, the shoe portions 508 and 514 will assume the illustrated clamping positions. Preferably, the horizontal guideway clamp 492 is arranged so that the crank part 498 is overcenter relative to the line of movement for rod 542 when the handle 494 is in the locked or clamping position. This renders the clamp 492 self-locking and enables the clamps to be maintained when the handle 494 is released.

The mode of clamping or aliixing one column with respect to the other column is demonstrated in FIGURES 1.6 and 17. Both of the vertical columns 464 and 470 are provided with tl-shaped ways S16 extending the length thereof, whereas both horizontal columns 452 and 458 i are formed with V-shaped ways 518. Additionally, the

V-shaped ways S18 are formed with a T-slot 520. These ways 516 and 518 and T-slot 520 coact with a double clamp 522 afforded at each intersection of a horizontal column with la vertical column and thereby securely maintain the relative positions of each set of intersecting columns. The double clamp 522 has a rotatably movable handle 524 formed with a screw portion 526 that isin threaded engagement with a wedge block 528 engaging one side of the V-shaped way 516. Between the handle 524 and the opposite side of the V-shaped way 516, a slidable wedge block 530 is positioned and appropriately guided with respect to the threaded wedge block 528, such that when the handle 524 is revolved, the threaded connection will cause the two wedge blocks 528 and 530 to move into tight engagement with the sides of the V- shaped way 51.6, In doing this, the wedge blocks 528 and 53@ climb the sides of the way 516, and this in turn causes a T portion 532 of the wedge blocks 528 and 530 to be moved into snug eng-agement with the sides of the T-slot 520 (see FIGURE i7). Hence, a double clamping action takes place securing the intersecting columns together simply by maneuvering a single handle. A springl biased detent 533 holds the handle 524 in the unlocked position shown by the dotted lline in FIGURE 17. y

The workpiece 2S is held in position on the vertical and horizontal columns by a series of individual workpiece holders 534 and S35 of a character depicted respectively in FIGURES 13a and 14. As displayed in FIGURE 13a, the horizontal workpiece holder 534 is fitted onto the ways 51S of the horizontal column 4518 for slidable movement and is clamped in place through the action of a T-bolt 536 threadedly engaged with a handle 538. When the handle is turned, the T-bolt will snugly engage the T-slot 52d in the manner previously described. At the upper part of the horizontal workpiece holder 534, an abutment S40 is formed against which the workpiece 28 is placed, and a clam-p screw 542 is then turned until the workpiece 2S is in tight engagement with the abutment 54).

The vertical part of the workpiece 28 is held in place by one or more of the FIGURE 14 vertical workpiece holders S35. These vertical workpiece holders 535, of course, may be identical with those used 4for the horizontal part of the workpiece if a T-slot is also provided in the ways 516. In the absence of a T-slot, two coacting wedge blocks 546 and 54S may be made adjustable both relative to each other and the ways 516. This enables the block 54S, for example, to be loosened and tightened for unclamping and clamping. As with the horizontal workpiece holders 534, the vertical workpiece holders 535 also have an abutment as that at 550 coacting with a clamp screw 552. l

The movement of the horizontal columns 452 and 458 up and down is facilitated by a counterweight arrangement shown in FIGURE ll. As there viewed, the upper part of the frame 442 on the left and right sides thereof has installed thereto double pulley sets 554 and 556. Cables 558 each have one end attached to opposite ends of the lower horizontal column `458 and the opposite ends extending around the double pulley sets 554 and 556 and attached to countenweights 560. Similarly, cables 562 are attached at opposite ends to the upper horizontal column 452 and counterweights 564 and extend around double pulley sets 554 and '556. The weights of the counterweights are selected so that the horizontal columns 452 and 45S are easily maneuvered, particularly upwardly and so that the eort required to overcome the weights in moving the horizontal columns 452 and 458 downwardly is not excessive.

When moving the horizontal columns 452 and 458 up and down, it is necessary that parallel alignment thereof be maintained, and also that each end of the horizontal columns 452 and 458 be normal to the adjacent guideway. Otherwise, when maneuvering either of the horizontal columns 452 or `45L up and down, tilting could occur and this makes it not only diiiicult to move the horizontal columns but also induces inaccuracies into the support alignment. For this purpose, an aligning arrangement is provided comprising a double pulley 566 (see FIGURE 13) revolvably supported at each end of the horizontal columns 452 and 458. These pulleys 566 coact through wires to maintain the desired alignment.

To understand this more clearly, reference is made to FIGURE ll and as shown, a wire 568 is attached at one end to the lower right part of the frame 442 at 57) and extends around the pulleys 566 |at each end of the lower horizontal column 458, and then upwardly to a point on the frame 442 in the vicinity of the left end of the upper horizontal column 452 where the opposite end of the cable 568 is attached at 572. A second lwire 574 has one end attached at 576 to the `frame 442, this point being near the left end of the -lower horizontal column 45S,

is wound around each of the pulleys 566 at the opposite ends of the horizontal column 45S, and then extends upwardly where it is attached at point 578 to the upper horizontal column 452. A third wire 580 starts at the point 582 at the upper left part of the frame 442, extends around the pulleys S66 on each end of the upper horizontal column l452 and is attached at 584 to the Ilower right part of the lower horizontal column 458. The fourth wire denoted by the numeral 586 starts at 587, extends around the pulleys 566 on each end of the upper horizonal column 452 and ends at point 588 on the lower horizontal column. With this system of wires and pulleys, as t-he horizontal columns 452 and 458 are maneuvered, each end thereof is maintained in strict alignment so that there is no tilting or cocking permitted.

Another Iaspect of this workpiece support 441 is the relationship of the cutting tool 26 to the workpiece 28. The cutting tool 26 preferably has helical utes thereon and, as mentioned before, this aids in causing the chips to be withdrawn along the spindle 24 by the vacuum system, and ialso lcontributes to the maintenance of the engagement between the housing 432 and the workpiece 28. This engagement eliminates the need for rigid support of the workpiece 28 on the side opposite the tool 26.

To aid is yaccurately positioning the workpiece, graduated scales 589 and 59) are provided in vertical and horizontal directions as viewed in FIGURE ll and 'are ailixed to the fname 442 so as to be adjacent pointers 592 and 594 movable with the columns.

The described workpiece support 441 by the system of moving the horizontal and vertical columns permits a workpiece 28 to be placed anywhere within the vareas defined by these columns; in other words, the workpiece 28 may be placed in a lower right corner of the frame 442, in the middle of the area provided therefor, -or at any other part thereof.

Before either operation can be commenced, there are certain adjust-ments. For instance, the proper size cutting too-l 26 must Ibe installed, for this size will determine the position of the photohead 172 -on .the arm 174 in relation to the axis of rotation of the motor 233. Also, the proper size reticle 156 must be selected to correspond to the t-ool size. After the mastery draft 134 is attached to the `draft table 132 and the required power turned on, the next step requires the balancing of the outputs from the `different sets of photocells in the previously described manner, i.e., by adjusting knob 206` so as to center the needle of -ammeter 204. v

OPERATIONAL SUMMARY As has Ebeen' previously mentioned several times, there are two aspects to the control -of the reproducing apparatus. One offers manual control, which is possible through a manual control system, and the other is automatically achieved through the automatic control system.

M anual Control Manual control requires that the manual-automatic switch 424 be open, and as a result, contacts 3021?, 302e', 2745i, 274d, and 226g wil-l be closed and cause the associated circuitry to be effective. Also, preferably the olfcourse error signal voltage -an'd its iniluence on relay 210 is eliminated idunin'g manual control so that the solenoid operated valve 98 will not be held closed, especially when the photohead 172 is a substantial distance olf-course. For this purpose, a switch (not shown) or the equivalent, may be installed `between the preamplifier 186 Vland the amplier 208. Before any movement of the cutting tool 26 relative to the workpiece 28 can take place, the speed control dial 512 must be maneuvered towards the On position so as to cause limit switch control 330 to render the solenoid operated valve 98 ineffective to block pressure fluid from the control units 66 'and 68. The corresponding speed control signals developed by the speed control potentiometers 318 and 320 will be supplied to both the automatic and manual steering control potentiometers 340 an'd 250, the manual steering potentiometer 340 only being effective. By now maneuvering lthe steering control dial 332, and while viewing the relative positions of the simulated cutter image and the image of `the contour line 136 on the TV viewer 164, appropriate X-axis and Y-axis control sign-al voltages can be developed by the manual steering potentiometer 340 and applied to the X- :and Y-axis summing circuits 112 and 116. It should be kept in mind that these X-axis and Y-axis control signal voltages also include the desire-d speed signal. These control signal voltages then are summed along with the oscillating and feedback signal voltages and corresponding summed regulating voltages determined by the gain potentiometers 392 and 392 'are applied to the amplifiers 114 Iand 118. These amplified regulating voltages are `delivered to the control units 66 and 68 whereupon the drive motors 54 and 60 cause movement respectively of the table 12 and the too-l support 18 such that the cutting tool 26 is moved along a desired path, the result-ant of the table and tool support movements. This desired path will, of course, coincide with the contour line 136 on the master draft 134 if tracing manually. Additionally, if the rapid traverse switch 398 is closed, the elimination of the feedback will permit the tool 26 to be maneuvered at a faster speed as has been indicated.

During manual operation lthe tracer mechanism `162 serves no function; however, the automatic steering shaft 242 ismaintained synchronized with the manual steering shaft 334 so that `at any time automatic control can be initiated without any lag or lost motion therebetween.

Automatic Control 

4. IN APPARATUS FOR REPRODUCING A CONTOUR OF A PATTERN ON A WORKPIECE, THE COMBINATION OF TOOL AND WORKPIECE SUPPORTS SO ARRANGED AS TO HAVE RELATIVE MOVEMENT IN TWO MUTUALLY TRANSVERSE PATHS, DRIVE MEANS FOR PRODUCING THE RELATIVE MOVEMENT OF THE SUPPORTS ALONG THE TWO PATHS, AND A TRACER MECHANISM ARRANGED TO HAVE MOVEMENT CORRESPONDING TO THE RELATIVE MOVEMENT BETWEEN THE TOOL AND WORKPIECE SUPPORTS, THE TRACER MECHANISM COMPRISING A PHOTOCELL MOUNTING MEMBER REVOLVABLY POSITIONED ON THE TOOL SUPPORT, A SERIES OF PHOTOCELLS ARRANGED ON THE MOUNTING MEMBER INCLUDING STEERING PHOTOCELLS ADAPTED TO SENSE PARALLEL MISALIGNMENT THEREOF RELATIVE TO THE CONTOUR AND TO DEVELOP CORRESPONDING STEERING ERROR SIGNALS AND ON-COURSE PHOTOCELLS ADAPTED TO SENSE OFF-COURSE DEVIATIONS THEREOF FROM THE CONTOUR AND TO DEVELOP A CORRESPONDING OFF-COURSE ERROR SIGNAL, A POSITIONING MOTOR REVOLVING THE PHOTOCELL MOUNTING MEMBER IN ACCORDANCE WITH THE STEERING ERROR SIGNALS SO AS TO CAUSE THE STEERING PHOTOCELLS TO IN PARALLEL ALIGNMENT WITH THE CONTOUR, FIRST MEANS MANEUVERABLE BY THE POSITIONING MOTOR SO AS TO DEVELOP A STEERING CONTROL SIGNAL REPRESENTING THE DIRECTION THE MOUNTING MEMBER IS REQUIRED TO BE REVOLVED BY THE POSITIONING MOTOR SO AS TO CORRECT FOR STEERING ERRORS, SECOND MEANS COMMUNICATING WITH THE ON-COURSE PHOTOCELLS AND MANEUVERABLE BY THE POSITIONING MOTOR SO AS TO DEVELOP AN OFF-COURSE CONTROL SIGNAL CORRESPONDING IN MAGNITUDE AND POLARITY TO THE OFFCOURSE ERROE SIGNAL, AND A SUMMING CIRCUIT COMMUNICATING WITH THE FIRST AND SECOND MEANS AND ARRANGED SO AS TO PRODUCE AN EQUIVALENT REGULATING SIGNAL FROM THE CONTROL SIGNALS FOR CONTROLLING THE OPERATION OF THE DRIVE MEANS SO THAT RELATIVE MOVEMENT OF THE SUPPORTS PRODUCED BY THE DRIVE MEANS WILL CAUSE THE CONTOUR OF THE PATTERN TO BE REPRODUCED ON THE WORKPIECE. 